The present invention relates generally to methods of making motor mounting systems arrangements that are particularly adapted for interconnecting a motor directly with a blower wheel and blower housing in a manner that provides improved isolation of torsional vibrations and yet also unfailingly provides stringent control of axial and tilting motor movements without excessively amplifying vibrations associated with such movements.
In direct drive blower applications (for example those designed for furnaces and in room air conditioning applications), many different motor vibration isolation schemes have been used in an effort to reduce the noise caused by vibrations transmitted from the motor to the blower housing and any associated connected duct work; or to a support in an air conditioner. Predominant single phase induction motor torsional pulsations or vibrations having a frequency that is equal to or to a multiple of twice the line frequency (for example 120 Hz for 60 Hz power supplies and 100 Hz for 50 Hz power supplies) are usually the source of the most objectionable noise in both of the above-mentioned applications and an effective but inexpensive noise isolation scheme for this vibration mode and frequencies is very much needed.
.Iadd.As described in W. J. Morrill U.S. Patent 2,928,961 (which issued Mar. 15, 1960), in the paragraph bridging columns 4 and 5 of the patent; another type of objectionable vibration that may be of concern is a low frequency vibration due to rotating mechanical unbalances. The fundamental or forcing frequency of these vibrations is the speed or frequency of rotation of the mechanical unbalance expressed in cycles or cycles per second (i.e., hertz) as opposed to revolutions per minute. Thus, in the words of the Morrill patent, a rotating mechanical unbalance would have a fundamental frequency of vibration of 13.3 cycles (hertz) when the motor shaft speed is 800 rpm (800 rpm=13-166 cps.times.60 sec./min). As recognized by Morrill in the last paragraph in column 1 of his patent, persons skilled in the art have known, long prior to the present invention, of the difficulties associated with designing motor mounting systems having sufficient mechanical rigidity to droop and mechanical unbalance variations. .Iaddend.
Blower wheels supported within blower housings typically are dimensioned and positioned so that relatively close running tolerances are maintained between each wheel and housing in the interest of maximizing blower efficiency. In direct drive applications, a motor is suspended from the blower housing scroll and the motor shaft in turn supports and drives the blower wheel within the housing. This type of direct drive arrangement is very desirable because of its relative simplicity and economy as compared to other arrangements (e.g., those that require separated components such as belts, pulleys, separate blower wheel bearing systems and supports, etc.). However, with prior direct drive arrangements, it has been necessary to use complex and expensive mounting arms and related parts in order to generally satisfy the requisites of good torsional vibration isolation and acceptable control of other motor movement.
It has long been known that motor vibrations or pulsations may be amplified during transmission to a blower housing, depending on the frequency of vibration and resonant frequency of the mounting system (or parts thereof). Thus, the resonant frequency of each part of such system should be considered in designing a mounting arrangement. However, direct drive blower motors also must be supported with sufficient stiffness or rigidity to prevent sagging or .[.dropping.]. .Iadd.drooping .Iaddend.of the motor and to prevent blower assembly damage from "shipping shock" tests or during actual shipping and handling. One primary problem exists because design efforts directed to minimizing the transmission of torsional mode vibrations may well increase the transmission of (or chance of amplification of) axial and tilting mode vibrations and may even excessively reduce the structural integrity of a given arrangement vis-a-vis shipping shock.
Generally speaking, it would be preferable to completely isolate axial mode and tilting mode motor vibrations from a blower housing in direct drive applications. However, the need to rigidly support the motor and blower wheel, and thus maintain a predetermined running clearance between blower parts, has not permitted the use of connections between the motor and blower housing that are sufficiently "soft" to provide such complete isolation.
Typical mobile home furnace blowers utilize motors rated at approximately 373 watts (0.50 hp) or more and having a mass of 5.9 kg (13 pounds) or more. On the other hand, even heavier and more powerful motors often are used in typical residences, offices, and shop areas that utilize air moving blowers. The larger mass of such motors requires even more rigid mounting members for avoidance of tilting problems and shipping shock damage than would be the case with motors of smaller mass such as those used, for example, for window fan applications (typically these motors are rated at 75 watts or less and have a mass of 2.2 kg or less).
Generally speaking, the larger the mass and power of the motor, the more difficult it is to resolve the above-mentioned problems; and solutions applicable to small motor applications are not always applicable to arrangements involving larger motors.
For example, many applicances that incorporate blower mounted motors are subjected to mechanical tests that simulate "shipping shock"--i.e., conditions that might occur during handling and shipping of such appliances. These conditions could be bouncing onto a truck loading dock, rough railway transit, etc. The actual form of the tests may vary for different appliance manufacturers and for different types of appliances. However, one commonly used test procedure is spelled out in a test sequence specification of the "National Safe Transit Committee" (sponsored and coordinated by the Porcelain Enamel Institute, Inc.) for packaged products of one hundred pounds or more. This sequence involves vertically vibrating the packaged product for at least 1 hour at a frequency such that the product will momentarily leave the vibrating table or platform during the vibration cycle; and then permitting movement of the packaged product along an inclined plane until a face or edge of the package impacts against a backstop. This impact test may be carried out with a "Conbur Incline" testing device or other equipment producing equivalent results and a specified shock recorder. Of course, other tests may take place with an appliance unpackaged. In any event, however, after the selected test or test sequence, the appliance itself (e.g., a furnace) is inspected for damage, and such inspection usually involves close scrutiny of any electrical motors to determine that the shafts thereof and mountings therefor have not been deleteriously affected.
Direct drive blower motors often are mounted so that the interface between the mounting means and the blower housing is located along or adjacent to a curved inlet or eye of the blower housing, such curved portion of the housing generally being less flexible and less apt to act as a sounding board for motor induced vibrations, and also being better able to withstand shipping shock that might tend to tear the motor from the housing. It thus would be desirable that any improved arrangements be such that attachment to a blower would be along the curved inlet thereof.
In the past, one approach for mounting motors directly to blowers has involved the use of lugs that were fixed (for example by bolts or by welding) to a motor frame. In some applications utilizing this approach, the lugs were fixed (for example by bolting or welding) directly to a blower housing or scroll without grommets; and in other grommets have been used. In still other blower applications, such lugs have been interconnected with the motor by means of a strap or band.
The general objectives of the mounting arrangements used heretofore have been to provide sufficient mounting rigidity to avoid excessive tilting and axial movement of the motor during operation and to withstand shipping shock, while also attempting to minimize the transmission of vibrations (particularly torsional mode vibrations) to the housing through the motor mounting members. Unfortunately, improvement of a given design for one of these characteristics frequently will have a negative affect on the other characteristics. In addition, it has sometimes been necessary to provide "internal packaging" for arrangements that are good noise suppressors. For example, temporary supplemental supports or pads may be provided in furnace blowers for transit purposes. These supports or pads then are discarded prior to putting the furnace (or other appliance) in operation. Thus, engineering compromises must be made even with the complex known mounting arrangements.
A single member lug arm approach has long been recognized as a preferable form of direct drive motor mount (from a cost standpoint), but such approach simply has not been satisfactory in practice for direct drive blower applications vis-a-vis good torsional mode vibration isolation in combination with good mounting rigidity. For this reason, among others, it has been necessary to use relatively complex mounting arrangements for those applications where maximum isolation of torsional mode noise was to be provided as well as sufficient structural strength to meet shipping shock tests. For example, one prior arrangement has required the use of costly resilient hubs or cushion ring isolators along with a multitude of other different parts that have been assembled together to provide a costly and complex mounting arm assembly.
One or two member lug mounts have also been devised that have been used with ultra-soft or ultra-resilient blower mounting pads or grommets. This particular type of approach, however, can create or aggravate still other problems such as those associated with: motor sag .Iadd.or droop.Iaddend.; reduced tilting mode resonant frequency with the result that such frequencies would fall into an amplification range; shipping and handling damage; and overcompression of the pads or grommets (due to the weight of the motor-blower wheel) accompanied with effective stiffening of such pads or grommets.
Although a number of different design and performance criteria have been discussed hereinabove as illustrative of the complexity of the factors that must be satisfied with direct drive motor mounting arramgements, it will be understood that numerous other considerations may further confound the search for a desirable solution to the direct-mounted motor problems mentiond hereinabove. One of these, for example, is the possibility that a given motor mounting arrangement might have to support a motor with its shaft vertical, horizontal, or at some specified angle therebetween in different applications.
Single member types of mounting arms or members for axial air flow fans have been shown in prior literature. For example, Anderson patent No. 1,781,155 shows a motor that is supported by three substantially flat and straight supporting arms, the shaft of which supports a propeller type axial flow fan. Propeller or disc type fan mounting arrangements somewhat similar to Anderson's are also shown in Seyfried patent No. 1,873,343 and Goettl patent No. 2,615,620. In Seyfried, leather, canvas, spring steel, and brass arms are mentioned; and in Goettl, curved arms having arcuate motor embracing portions are illustrated.
Although it is desirable to utilize one piece mounting arms for direct drive blower motors, competitive economics would favor the permanent attachment of such arms to a motor shell during manufacture of the motor. However, for designs having very long arms, increased packaging costs and shipping costs due to increased package volume can offset the cost savings associated with single arm construction. Furthermore, while lengthy arms of the type shown by Seyfried, Anderson, etc. may be made from a choice of different materials (as described, for example, by Seyfried) and have satisfactory strength and torsional vibration transmissibility characteristics; prior attempts to utilize flat single member supports for direct drive blower motors have resulted in mounting arrangements having either unsatisfactory strength characteristics or unsatisfactory torsional vibration transmissibilities.
To be more explicit; it can be assumed that the arms of Goettl, Seyfried, or Anderson (referred to hereinabove) would have sufficient strength to resist failure in either a tensile mode or buckling mode when supporting a propeller fan motor of given mass during a particular test. However, if those arms were shortened to permit mounting of the same motor in a blower housing inlet, even though the arms would still be sufficiently strong to not tear or buckle, the torsional mode vibration transmissibility of such arms would be objectionably increased. For example, an arm shortened from an effective radial extent of about 7.21 inches to an effective radial extent of about 2.2 inches would have a substantially greater transmissibility via-a-vis 120 hz torsional mode vibrations. On the other hand, if the shortened arms were then further modified by being reduced in thickness and axial width in order to obtain a low transmissibility for torsional vibrations, their resistance to buckling would be reduced about 69%, and their resistance to failure due to tensile stresses would be reduced about 88%.
Accordingly, it would be desirable to provide new and improved methods of making motor mounting systems and arrangements that include relatively short single member mounting arms, motors incorporating the same that are low cost in terms of total material and total labor involved therewith, and yet wherein the resulting systems and arrangements are at least satisfactory if not improved in terms of noise isolation and structural reliability. It would also be desirable to provide methods of making such arrangements that could be easily adapted for use with motors having different housing configurations or that are to be mounted with different shaft orientations.
Accordingly, it is a general object of the present invention to provide new and improved methods of making motor mounting arrangements and systems whereby the abovementioned and other problems may be solved.
It is a more particular object of the present invention to provide new and improved methods of making motor mounting arrangements, and systems .[.of.]. that have good resistance to shipping shock damage even without supplemental or internal packaging, a high degree of rigidity vis-a-vis axial and tilting mode vibraions, and low transmissibility for torsional mode vibrations.
It is a further object of the present invention to provide new and improved methods of making the above-mentioned arrangements and systems, that may be utilized to solve the above-mentioned and other problems, and that may be quickly and easily fastened to a blower or other type of housing.